One of our favorite features of Firefox (and Chrome) is the undo closed tab option, a feature that resurrects an accidentally closed tab via your History menu or keyboard shortcut (Ctrl+Shift+t [Windows] or Cmd+Shift+t [Mac]); if you accidentally closed a whole window, on the other hand, you were out of luck. According to Mozilla Links, however, the nightly builds of Firefox 3.5 Beta 4 (which will most likely drop sometime this week) include a new Recently Closed Windows entry in the History menu that will allow you to restore accidentally closed windows. We're in heaven! Update: As many readers were very quick to point out in the comments, this feature is already available in Opera and Chrome. [Mozilla Links]